Vegetable fibers are used in a wide variety of fields and various proposals have been made with respect to methods of their production. Methods of producing fiber using, for example, bamboo as the vegetable material have already been proposed by the present inventors. For example, a method of producing bamboo fiber is disclosed in Japanese Patent Laid-Open No. 4-216007 (UK 2 251 002 in part), including: a first step of crushing a bamboo material along the growing direction of the bamboo by means of a rolling mill; and a second step of opening up the bamboo material obtained from the first step by sending it by means of a feed roll to an opening device which has a rotary drum with a large number of teeth. Further, in the specification of Japanese Patent Laid-Open Application No. 5-138617 (UK 2 251 002 in part), a method of producing bamboo fiber has been proposed, including: a first step of crushing a bamboo material along the growing direction of the bamboo by means of a rolling mill; a second step of opening the bamboo material obtained at the first step by a rag opener; and a third step of forming the bamboo material obtained at the second step into fine fibers by means of a turbo-mill. These are methods for producing bamboo fibers in a quick and efficient manner.
It has been found, however, that, when the bamboo fibers obtained by the above methods are blended with a cement and formed into a bamboo fiber-cement formed body, there is about a 15% difference in the flexural strength of the obtained formed body between the case of using the bamboo fibers with a thin peel portion at the inside of the bamboo material and the case of using the bamboo fibers with the thin peel portion removed. The bamboo fiber without the thin peel portion is superior in this regard. For this reason, in the specification of Japanese Patent Application No. 4-177070 (UK 92 25711.6), the present inventors have furthermore proposed a method of producing bamboo fiber, including: a first step of crushing a bamboo material along its growing direction by means of a rolling mill; a second step of forming the crushed product obtained at the first step into fibers by means of a hammer mill type crusher having a certain mechanism; and a third step of removing the thin peel portion inside the bamboo material that is mixed into the bamboo fibers obtained at the above second step.
However, when using the bamboo fibers obtained by these methods to produce a bamboo fiber-cement formed body or the like, blending of the bamboo fibers with other materials is necessary as described above. However, if the dispersibility of the bamboo fibers is inferior, there are the disadvantages that a uniform blending with the other materials is difficult to obtain or production efficiency is low because it takes time to obtain a uniform mixture. Particularly, if the fiber diameter of the bamboo fibers is thin, the fibers tend to entwine around each other to hamper homogeneous mixing with the other materials. Thus the superior reinforcing effect possessed by vegetable fibers has not been fully utilized.
Accordingly, a method using a surface-active agent, for example, has been proposed as a method for improving the dispersibility of vegetable fiber when the vegetable fibers are in the form of a slurry in a large amount of water. However, the methods to be used in cases where a surface-active agent is not desirable and methods for improving the dispersibility of vegetable fiber when blending is effected in a half-wet state have not been developed heretofore.
Accordingly, it is an object of the present invention to provide a method and apparatus for improving the dispersibility of vegetable fibers in order to produce vegetable fibers having a high dispersibility that can be easily blended with other materials.